This invention relates generally to gas turbine engines and more particularly to swirler assemblies for supplying compressed air to the combustor of such engines.
A gas turbine engine includes a compressor that provides pressurized air to a combustor wherein the air is mixed with fuel and ignited for generating hot combustion gases. These gases flow downstream to one or more turbines that extract energy therefrom to power the compressor and provide useful work such as powering an aircraft in flight. Fuel is typically supplied to the combustor through a plurality of fuel nozzles positioned at one end of the combustion zone. The air is supplied through surrounding assemblies, known as swirler assemblies, which impart a swirling motion to the air so as to cause the air and fuel to be thoroughly mixed. The swirler assemblies are mounted in a dome plate that is joined to the upstream ends of the combustor""s inner and outer liners, and each fuel nozzle tip is received in a corresponding one of the swirler assemblies.
The swirler assemblies have to endure vibratory stresses due to fluctuating flows and pressures of the air stream that exits the compressor. The vibrations cause alternating stresses in combustor components and can lead to high cycle fatigue failures in parts that are not otherwise highly stressed from thermal or pressure loading. One conventional swirler assembly comprises a primary swirler and a separate secondary swirler. The primary swirler has a plurality of circumferentially spaced swirl vanes or air passages. The vanes or passages are angled with respect to the axial centerline of the swirler assembly so as to impart a swirling motion to the airflow. The secondary swirler also has a plurality of circumferentially spaced swirl vanes or air passages. The vanes or passages of the secondary swirler are angled so as to produce a swirl of air swirling in the same or opposite direction as the primary swirler to further promote fuel-air mixing. The primary swirler is disposed in sliding engagement with the secondary swirler, which is fixedly mounted to the dome plate. This arrangement allows the primary swirler to receive the fuel nozzle and accommodate relative motion between the fuel nozzle and the dome plate.
A retainer fits over the primary swirler and is welded to the secondary swirler to retain the two swirlers in engagement with one another. One type of retainer is stamped out of sheet metal into a circular annulus. However, the airflow through the vanes or passages of the primary swirler creates a reaction force that tends to cause the primary swirler to rotate with respect to the secondary swirler and the fuel nozzle. If allowed to rotate, the primary swirler would fail to impart the necessary level of swirling to the air, and effective mixing of the air and fuel would not be achieved. Furthermore, rotation of the primary swirler could cause excessive wear to the fuel nozzle tip. Primary swirler rotation is thus prevented in conventional swirler assemblies by providing at least one outwardly extending tab on the primary swirler that engages a stationary structure on the secondary swirler so as to limit relative rotation of the swirlers.
In combustors with swirler assemblies that are relatively closely spaced, two anti-rotation tabs can be used for each swirler assembly. The use of two anti-rotation tabs provides more contact area than single tab arrangements and thereby reduces wear. To accommodate swirler assemblies with two anti-rotation tabs, the annular, single piece retainer is replaced with a pair of retainer segments. The retainer segments are each less than 180 degrees in length and are welded to the secondary swirler in a cantilevered fashion. Retainer segments are subject to weld joint cracking due to non-uniform pressure flow variations that cause vibratory excitation of the retainer segments. Most typically, such cracking initiates in the ends of the retainer segments. Failed retainer segments can cause unscheduled engine removals to retrieve primary swirlers that become free when fuel nozzle maintenance is performed.
Accordingly, there is a need for an improved swirler assembly having more durable retainer segments.
The above-mentioned need is met by the present invention that provides a swirler assembly having first and second members disposed in sliding engagement with each other. The two members are maintained in sliding engagement by one or more retainer segments joined to the second member and engaging the first member. The retainer segment is an arcuate member defining inner and outer curved edges and first and second ends. Each end has a concave cutout formed therein to reduce weld joint and bending stresses that occur from the forced vibration of the retainer segment.
The present invention and its advantages over the prior art will become apparent upon reading the following detailed description and the appended claims with reference to the accompanying drawings.